[tree-ssa] DCE and conditionals

[Andrew MacLeod]

On Mon, 2003-05-05 at 17:23, law@redhat.com wrote:
> In message <1052169493.19625.1284.camel@p4>, Andrew MacLeod writes:
. 
>  >> > 
>  >> PHIs that have all their arguments the same can be easily checked in the
>  >> linearizer.
>  >> 
>  >
>  >But they aren't the same until I've coalesced them, and rewritten them,
>  >and then we are out of SSA form... So having it in the linearizer does
>  >do us much good in these cases.
> Copy prop along with various edge eliminations can result in cases where
> PHI nodes can turn into copies.   There's a couple cases:
> 

Perhaps I should be explicit :-). Having it in the linearizer alone
doesn't help the cases Im currently interested in :-).  Anyway, we'll
deal with this once I get all the code checked in.

>   1. All the source operands are the same.
> 
>   2. There are two unique source operands, one of which is the same
>      as the destination operand.
> 
> When I played with this stuff at the RTL level, the only way you'd see
> these things occuring was if you allowed overlapping ranges for 
> registers in PHI nodes during value numbering/copy propagation.
> 

And we are about to do that very shortly...


Andrew